Joy Boy

Joy Boy was a man from the Great Kingdom born 900 years ago at the start of the Void Century, as well as the first pirate in history. An extremely relevant figure in the Void Century, Joy Boy played an important role in the history of Fish-Man Island and left behind a certain item of unimaginable value on the last island of the Grand Line, thus becoming a legendary and remembered figure in the world.

He was first mentioned on the Poneglyph read by Nico Robin while at the Sea Forest.

(Source: One Piece Wiki)